The present invention is directed to a high-capacitance varistor having two chip components, in particular a multi-layer varistor and a multi-layer capacitor, wherein respectively two end faces opposed from one another are metallized terminal surfaces.
Varistors are non-linear, voltage-dependent resistors whose value of resistance decreases with increasing voltage. Varistors are mainly used for over-voltage protection. As a result of the varistor effect, which occurs when a pre-selected voltage is reached, further build-up of an over-voltage is prevented and the voltage is limited to values that lie just above an operating voltage.
Prior art metal oxide varistors have a relatively high self-capacitance of approximately 20 nF. However, with regards to over-voltage protection an even greater capacitance is desirable because the resultant low-pass filter characteristic smoothes steep over-voltage edges and thus improves the protective level of the varistor.
It is known to improve the protective function of varistors, for example in view of noise peaks in motor vehicle engines, in that a varistor and an additional capacitor are connected in parallel as wired, discrete components. However, this traditional high-capacitance varistor is still not acceptable because it doubles the space requirement on a printed circuit board and because assembly costs are double in comparison to a normal varistor.
Varistors are also known in the prior art that have an especially high self-capacitance that is attributed to a high proportion of strontium titanate in the varistor ceramic. However, such varistors also only have capacitances below approximately 100 nF, which is inadequate for a sufficient smoothing of, for example, noise spikes in motor vehicle engines.